Analytical modeling of dual-junction tandem solar cells based on an InGaP/GaAs heterojunction stacked on a Ge substrate

An analytical model is used to describe the elctrical characteristics of a dual-junction tandem solar cell performing a conversion efficiency of 32.56% under air mass 1.5 global (AM1.5G) spectrum. The tandem structure consists of a thin heterojunction top cell made of indium gallium phosphide (InGaP) on gallium arsenide (GaAs), mechanically stacked on a relatively thick germanium (Ge) substrate which acts as bottom cell. In order to obtain the best performance of such a structure, we simulate for both the upper and lower sub-cell the current density-voltage, power density-voltage, and spectral response behaviours taking into account the doping-dependent transport parameters and a wide range of minority carrier surface recombination velocities.